FURTHER SUPPORT FOR A MIOCENE PALEOCHANNEL ACROSS THE SIERRA NEVADA CREST BETWEEN BRIDGEPORT AND HETCH HETCHY, CA

Intra-canyon lavas and tuffs of the Stanislaus Group (Table Mountain Formation, Eureka Valley Tuff, and Dardanelle Formation) have long been used to argue for Miocene east-side-up tilting and uplift of the Sierra Nevada, CA. Here we extend documentation of Stanislaus Group in a previously poorly-studied part of its areal extent - south and southwest of the source at Little Walker Caldera, down-paleochannel at Rancheria Mountain. We used lithology plus paleomagnetic and geochemical analysis for correlation between outcrops, along with geological mapping to improve upon previous studies. Together, these and previous data strongly indicate a southwest-flowing paleodrainage system linking these outcrops that extended across what is now the Sierra Nevada crest. We also document a number of elements of the surrounding andesitic lavas and tuffs of the Mehrten Formation (Relief Peak formation when older that Stanislaus and Disaster Peak when younger). In addition, we analyzed paleomagnetic samples from the Stanislaus Group Reference Section along the West Walker River and document an unknown tuff that had previously been lumped in with the Eureka Valley Tuff Upper Member. This result could explain disagreement between some previous measures of vertical axis rotation in the region, since comparing two different tuffs as if they were the same would cause spurious declination and inclination anomalies.